This invention relates to a device for controlling the selection of needles, intermediate jacks, or selecting jacks, in a circular knitting machine, in particular a hose knitting machine.
It is known that that selection is generally effected by means of slides arranged in banks or packages and selectively movable in their length direction to engage or not to engage butts of selecting jacks, or intermediate jacks, or needles. The selective movement of the slides is derived from a pattern drum provided with pegs or teeth on its lateral surface in accordance with a knitting program and being moved forward stepwise by means of a ratchet mechanism which engages with a peripheral serration on the drum periphery.
Also known is that in general the drum forward movement must be of one or two steps at a time, which complicates the construction of the drive device.
A device of the type outlined above, which selectively allows a one or two-step forward movement, is described in my U.S. Pat. No. 4,226,096.
In that device, the drive for the pattern drum forward movement ratchet pawl is derived from a ring cam rigid with the needle cylinder (or lower needle cylinder) of a circular knitting machine, the cam being formed with a special profile which includes a first portion with a gently increasing radius and second portion with a sharply increasing radius. Engaged with the cam profile is a rocking lever whereto the ratchet pawl is pivoted. Also provided is a programmed control means for disengaging the ratchet pawl from the teeth of the drum serration while the first portion of the ring cam is operative, such as to produce a single step forward movement, whereas when such disengagement means is not activated the ratchet pawl produces a two step forward movement.
Such a device has a simpler construction than prior devices and becomes operative in timed relationship with a cylinder, in either modes of forward movement. It has been found, however, that it poses some problems when it is desired that the selection capabilities be extended without substantially altering the construction of the device and the pattern drum with its related program.